1. Field of the Invention
The present invention relates to fluid systems. The invention concerns, more particularly, an internal filter assembly for a fluid system that restricts the movement of particulates located within the fluid system.
2. Description of Background Art
Articles of athletic footwear conventionally include two primary elements, an upper and a sole structure. The upper securely and comfortably receives the foot and is conventionally formed of foam, leather, and textile materials that are sewn or adhesively bonded together. The sole structure conventionally includes multiple layers that are referred to as an insole, midsole, and outsole. The insole is a thin, padded member located adjacent to the foot that improves the comfort of the footwear. The midsole forms the middle layer of the sole and often includes a resilient, foam material, such as polyurethane or ethylvinylacetate, that attenuates impact forces and absorbs energy when the footwear makes contact with the ground. The outsole is generally fashioned from a durable, wear resistant polymer and includes texturing to improve traction.
A midsole may also incorporate a fluid-filled bladder that provides enhanced impact force attenuation and energy absorption, as disclosed in U.S. Pat. No. 4,183,156 to Rudy, hereby incorporated by reference. Bladders of this type may include a plurality of chambers that are in fluid communication and extend throughout the heel portion or the forefoot portion of the midsole, for example. U.S. Pat. No. 4,219,945 to Rudy, also incorporated by reference, discloses a fluid-filled bladder encapsulated within a foam material. The combination of the bladder and the encapsulating foam material functions as a midsole. An upper may be attached to the upper surface of the encapsulating material and an outsole or tread member may be affixed to the lower surface, thereby forming an article of footwear.
Another type of prior art bladder utilized in footwear sole structures is disclosed in U.S. Pat. Nos. 4,906,502 and 5,083,361, both to Rudy, and both hereby incorporated by reference. The bladders are formed as a gas-pressurized structure that includes a hermetically sealed outer barrier layer that is securely bonded substantially over a double-walled fabric core. The double-walled fabric core has first and second outer fabric layers that are normally spaced apart from one another at a predetermined distance. Connecting members, potentially in the form of multi-filament yarns having many individual fibers, extend internally between the proximal or facing surfaces of the respective fabric layers. The individual filaments of the connecting members are anchored to the respective fabric layers to form tensile restraining means. A suitable method of manufacturing the double walled fabric structure is double needle bar Raschel knitting. U.S. Pat. Nos. 5,993,585 and 6,119,371, both issued to Goodwin et al., and both hereby incorporated by reference, disclose a fluid-filled bladder utilizing a double-walled fabric core, but without a peripheral seam located midway between the upper and lower surfaces of the bladder. Instead, the seam is located adjacent to the upper surface of the bladder. Advantages in this design include removal of the seam from the area of maximum sidewall flexing and increased visibility of the interior of the bladder, including the connecting yarns.
Fluid systems may also be incorporated into footwear sole structures to achieve a variety of benefits, including enhanced cushioning, improved fit, or ventilation of the upper. With respect to cushioning fluid systems, U.S. Pat. Nos. 5,558,395 and 5,937,462 to Huang disclose systems that utilize ambient air to pressurize one or more bladders located within the midsole. One-directional valves, also referred to as check valves, permit a fluid to enter a pump or fluid system but prevent, or check, fluid flow in the opposite direction. U.S. Pat. No. 4,446,634 to Johnson et al. and U.S. Pat. No. 5,794,361 to Sadler disclose self-contained fluid systems that include two bladders in fluid communication. The bladders are joined by conduits that include valves for directing fluid flow. With respect to ventilation, U.S. Pat. No. 6,085,444 to Cho discloses an article of ventilated footwear having a series of bladders and one-directional valves that draw outside air into the system and then discharge the air into the upper, thereby reducing or eliminating the presence of moisture in the area immediately surrounding the foot.
The fluid systems discussed above utilize a variety of valve types to direct fluid flow within the systems. U.S. Pat. No. 5,144,708 to Pekar and U.S. Pat. No. 5,564,143 to Pekar et al. disclose one-directional valves suitable for some fluid system applications. The valves each include two polymer layers connected along opposite sides to form a channel between the layers. The primary mechanism that checks or limits fluid flow is contact between the layers. Accordingly, particulates that become trapped between the layers may prevent the layers from making sufficient contact, thereby decreasing valve functionality. Fluid systems may be manufactured that incorporate a bladder having a double-walled fabric core. Loose fibers or portions of fibers that are present within the core, for example, are one source of particulates that may obstruct the operation of two layer valves.